Radiation-induced defects in quartz. III. Single-crystal EPR,ENDOR and ESEEM study of a peroxy radical

The X- and W-band single-crystal electron paramagnetic resonance spectra of an electron-irradiated natural quartz permit quantitative analysis of a ²⁹Si hyperfine structure (A ~12.6 MHz) and an ²⁷Al hyperfine structure (A ≤ 0.8 MHz) for a previously reported hole-like center. The ²⁹Si hyperfine structure arises from interaction with two equivalent Si atoms and is characterized by the direction of the unique A axis close to a Si–O bond direction. The ²⁷Al hyperfine structure, confirmed by pulsed electron nuclear double resonance and electron spin echo envelope modulation spectra, is characterized by the unique A axis approximately along a twofold symmetry axis. These ²⁹Si and ²⁷Al hyperfine data, together with published theoretical results on peroxy radicals in SiO₂ as well as our own density functional theory (DFT) calculations on model peroxy centers, suggest this hole-like center to have the unpaired spin on a pair of oxygen atoms linked to two symmetrically equivalent Si atoms and a substitutional Al³⁺ ion across the c-axis channel, a first peroxy radical in quartz. The nuclear quadrupole matrix P also suggests that the Al³⁺ ion corresponds closely to the diamagnetic precursor to the [AlO₄]⁰ center. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The influence of topography and land use on water quality of Xiangxi River in Three Gorges Reservoir region

A self-organizing map (SOM) was used to cluster the water quality data of Xiangxi River in the Three Gorges Reservoir region. The results showed that 81 sampling sites could be divided into several groups representing different land use types. The forest dominated region had low concentrations of most nutrient variables except COD, whereas the agricultural region had high concentrations of NO₃N, TN, Alkalinity, and Hardness. The sites downstream of an urban area were high in NH₃N, NO₂N, PO₄P and TP. Redundancy analysis was used to identify the individual effects of topography and land use on river water quality. The results revealed that the watershed factors accounted for 61.7% variations of water quality in the Xiangxi River. Specifically, topographical characteristics explained 26.0% variations of water quality, land use explained 10.2%, and topography and land use together explained 25.5%. More than 50% of the variation in most water quality variables was explained by watershed characteristics. However, water quality variables which are strongly influenced by urban and industrial point source pollution (NH₃N, NO₂N, PO₄P and TP) were not as well correlated with watershed characteristics.     

Application of Fractal Models to Distinguish between Different Mineral Phases

Fractal modeling is demonstrated to be an effective and rapid tool to distinguish between mineral phases in rock samples. It supplements work that previously could be performed only by observing the interpenetrational or metasomatic phenomena between different minerals with the aid of mineralographic microscope. The Gejiu tin district in southwestern China was chosen as a study area for the recognition and characterization of the spatial distribution of two phases (Types I and II) of cassiterite. Vector patterns used for this study were extracted from digital photomicrographs and analyzed with the aid of MapGIS. Perimeter–area fractal dimension, cumulative number–area exponent, and shape index were determined in order to quantify geometrical irregularities and spatial cassiterite phase distribution characteristics. The results show that fractal dimensions based on area and perimeter are larger for crystals of Type I than for those of Type II. The mean shape index (SI) increases from 0.54 (Type I) to 0.64 (Type II), indicating an increase in regularity. The number–area exponent also increases from 0.88 to 1.15, indicating the smaller crystals of Type II. The cumulative number–shape index log–log plot shows two separate straight-line segments. One of these probably represents a background shape realized during the original process of natural crystallization, whereas the other likely represents anomalous shapes because of weathering or other superimposed processes. Two parallel lines can be constructed on the perimeter–area log–log plots. The upper line, with a larger intercept, represents crystals with lower SI. The lower line represents crystals with higher SI, indicating that the intercept provides a measure of the irregularity of grains. By combining the perimeter–area model with cumulative number–area plot and shape index, the two phases of cassiterite can be distinguished and characterized. One phase has fewer crystals of large size, and the other has smaller crystals. This difference can be explained by assuming that under higher-temperature conditions, the large cassiterite crystals formed earlier than the smaller crystals. Consequently, the large cassiterites underwent longer, high-intensive weathering than the small crystals so that their shapes became more irregular. The younger, more abundant small cassiterites retained their original regular shapes.     

Fractal analysis of quartz grain boundary sutures in a granite (Malanjkhand,Central India) — Implications to infer regional tectonics

In the present paper the intensity of serration of quartz grain boundary sutures in the Palaeoproterozoic age Malanjkhand granite (Central India) is quantified using the ruler method of fractal analyses. The northern margin of the granite has proximity to the Central Indian Suture (CIS) that forms the southernmost part of Central Indian Tectonic Zone (CITZ) along which amalgamation of the northern and southern Indian shields took place. The fractal dimension (D) of the quartz sutures is calculated in 13 samples collected at varying distance from the CIS. D values are noted to increase in samples towards the CIS. This demonstrates the influence of the tectonic events along the CIS on fabric development in the Malanjkhand granite. Magmatic fabric defined by preferentially oriented feldspar laths and high-T solid-state deformation fabrics are observed in areas distant from the CIS. In contrast, mylonites and low-T fabrics such as bulging quartz grain boundaries occur in proximity to the CIS. It is inferred that the emplacement and high-T fabric development in the Malanjkhand granite was synchronous with regional accretionary processes that occurred in the region during the Palaeoproterozoic. Two different possibilities, one involving a single tectonic event and the other involving multiple tectonic events are discussed to explain the superimposition of low-T over high-T fabric due to which intensity of quartz grain boundary serration increases towards the CIS.     

Hydrothermal pattern of frozen soil in Nam Co lake basin,the Tibetan Plateau

Hydrothermal processes and the regimes of frozen soil formed in alpine regions with glaciers and lake area are complex and important for ecological environment but have not been studied in Tibet. Based on soil temperature and moisture data from October 2005 to September 2006 collected in the Nam Co lake basin, Tibetan Plateau (TP), those questions were discussed. The mean annual air temperature was −3.4°C with 8 months below 0°C. Air and soil temperature varied between −25.3~13.1°C and −10.3~8.8°C, respectively. Soil moisture variations in the active layer were small with the minimum value of 1.4%, but were influenced greatly by snowmelt, rainfall and evaporation, varying up to 53.8%. The active layer froze later, thawed earlier and was thinner, however, the lower altitude limit of permafrost is higher than that in most areas of TP. The effects of soil moisture (unfrozen water content) on soil temperature, which were estimated through proposed models, were more significant near ground surface than the other layers. The surface soil temperature decreased with snowcover, the effect of cold snow meltwater infiltration on soil thermal conditions was negligible, however, the effect of rainfall infiltration was evident causing thermal disruptions.     

Proximal and distal styles of pegmatite-related metasomatic emerald mineralization at Ianapera,southern Madagascar

The Ianapera emerald deposit is located in the Neoproterozoic Vohibory Block of southern Madagascar. The local geology consists of intercalated migmatitic gneissic units and calcareous metasedimentary rocks, containing boudinaged metamorphosed mafic/ultramafic lenses, all intruded by pegmatite veins. These units occur near the hinge of the tightly folded Ianapera antiform, within a few kilometers of the Ampanihy shear zone. Emerald mineralization is hosted by metasomatic phlogopite veins, and bodies developed within the mafic/ultramafic rocks. Based on field and textural relationships, we distinguish proximal and distal styles of mineralization. Proximal mineralization occurs at the contact of pegmatite veins with mafic/ultramafic units; in the distal style, pegmatites are not observed. Three types of emeralds could be distinguished, mainly on the basis of color and mineral zoning. Some of these emeralds have the most Al-depleted and Cr-rich composition ever recorded. Another characteristic feature to the Ianapera deposit and, to our knowledge, yet unreported, is the association of some emeralds with scapolite in metasomatised mafic rocks. Mineral inclusions are common in most emeralds and include phlogopite, carbonates, barite, K-feldspar, quartz, pyrite, zircon, monazite, bastnaesite, phenakite, plus Fe and Cr oxides. However, feldspar and rare earth element-bearing minerals occur predominantly in proximal emeralds, which also have a more incompatible trace-element signature than distal emeralds. We propose a model related to syn- to post-tectonic magmatic-hydrothermal activity. Pegmatitic bodies intruded units of the Ianapera antiform probably during tectonic relaxation. Exsolution of fluids rich in halogens and incompatible elements from the cooling pegmatites caused hydrothermal metasomatism of Cr-bearing mafic/ultramafic rocks in direct contact with the pegmatites. Local fracturing favored fluid infiltration, permitting the formation of distal mineralization. Emerald composition was controlled by the chemistry of the host rock. The presence of carbonate mineral inclusions in the emeralds and the high F-activity indicated by elevated F-contents in newly formed minerals suggest transport of Be as a fluoride-carbonate complex. It seems likely that beryl formation was triggered by precipitation of F-rich phlogopite, which removed the complexing ligand from the fluid.     

Life in the sublittoral zone of long-lived Lake Pannon: paleontological analysis of the Upper Miocene Szák Formation,Hungary

Life and depositional environments in the sublittoral zone of Lake Pannon, a large, brackish Paratethyan lake from the Late Miocene, were reconstructed from fossils and facies of the Szák Formation. This formation is exposed in several, roughly coeval (9.4–8.9 Ma) outcrops, located along strike of the paleo-shelf-break in northwestern Hungary. The silty argillaceous marl of the formation was deposited below storm wave base, at 20–30 to 80–90 m water depth. The abundance of benthic organisms indicates that the bottom water was usually well oxygenated. Interstitial dysoxia, however, may have occurred immediately below the sediment–water interface, as evidenced by occasional preservation of trace fossils such as Diplocraterion. The fauna comprised endemic mollusks, including brackish cockles of the subfamily Lymnocardiinae, dreissenid mussels (Congeria), and highly adapted, uniquely large-sized deep-water pulmonate snails (planorbids and lymnaeids). Ostracods were dominated by endemic species and, in some cases, endemic genera of candonids, leptocytherids, cypridids, and loxoconchids. Fish remnants include a sciaenid otolith and the oldest skeletal occurrence of Perca in Europe. The phytoplankton comprised exclusively endemic coccolithophorids, mostly endemic dinoflagellates (prevailingly Spiniferites), and cosmopolitan green algae. The Late Miocene fauna and flora of Lake Pannon were in many ways similar to the modern Caspian biota, and in particular cases can be regarded as its precursor.     

Eclogite relics in the Variscan orogenic belt of Bulgaria (SE Europe)

Eclogitic rocks were sampled from two zones in the basement of the Sredna Gora terrane (central western Bulgaria): (1) partially retrogressed eclogites and amphibolites embedded in sillimanite-bearing garnet-micaschists with kyanite relics and migmatites and (2) banded amphibolites associated with muscovite-bearing metagranites within two-mica paragneisses. Rutile relics and oligoclase + green hornblende + epidote ± biotite pseudomorphs after garnet suggest an eclogite facies event. A tholeiitic, transitional affinity was determined for the protoliths, suggesting a continental rift environment, consistent with several eclogite-bearing complexes in the eastern segments of the Variscan belt that arose from the Cambro-Ordovician Gondwana break-up. Decreasing pressure after the eclogite overprint was demonstrated by (a) diopside-albite symplectite, and (b) plagioclase + red–brown to green amphibole kelyphite. The early static re-equilibration, dated to 398 ± 5.2 Ma by ⁴⁰Ar–³⁹Ar technique, was followed by an amphibolite facies foliation, which was pervasive in amphibolites, gneisses and micaschists, and poorly developed in eclogites. The lithospheric PT paths corresponding to higher and lower metamorphic gradients reflect the juxtaposition of crustal and lithospheric mantle units, respectively. In the build-up of the basement of the Balkan orogen, the physical properties of the lithological complexes might have influenced the collisional pattern of involved microplates.     

Grassroots “flexible specialisation” in Brisbane’s West End: towards a politics of economic possibility

The focus on ‘flexible specialisation’ in the 1980s and 1990s marked an important turning point in framings of economic agency and diversity within economic geography. This article deconstructs the ways in which subjects were framed as ‘flexible’ in both the flexible specialisation literature and later work on the Diverse Economy (Gibson-Graham 1996, 2002, 2006), seeking out particular examples of the ways in which different projects of subjection appear to frame different views of economic possibility. Drawing richly on a case study of residents in an inner-city neighbourhood of West End, Brisbane (Australia), this paper uses resident’s articulations of their everyday practices to reinvigorate some of the ideas of the flexible specialisation literature and challenge, defamiliarise and rework existing ideas of economic life in “First World”, urban contexts.     

Youth empowerment and information and communication technologies: a case study of a remote Australian Aboriginal community

In spite of a ‘digital divide’, Aboriginal groups in Australia, as internationally, are increasingly using information and communication technologies (ICTs) to maintain their cultures, communicate, archive knowledge, empower their communities, develop skills and generate income. Each community uses the technologies differently in accordance with their particular needs and the opportunities available. The use of ICTs in Aboriginal youth empowerment is illustrated through a case study of an initiative undertaken by the Walkatjurra Cultural Centre in Leonora, remote Western Australia. A participatory process was used to engage the Centre’s young people and they were given individual assistance to develop their ICT related capacity. The community conceives this youth empowerment to be part of a broader youth participation process that will contribute to the Centre’s overall objectives.